Liquid substances applied to the airfoil surfaces of aircraft to prevent their freezing and being covered with ice in inclement weather are well-known and are important to ensure safe and proper takeoff of aircraft in winter. It is also well-known that aircraft departures are often delayed under such conditions and the anti-icing formulations must often be reapplied if the plane must wait an extended period. These liquids must also be stable not only through temperature extremes, but also during the taxiing phases of the takeoff procedure and thus must adhere to the wing surfaces during travel and ground winds.
Deicing solutions based upon ethylene glycol and water have been used for many years to remove ice, frost and snow from aircraft surfaces, however, since they have low viscosities, they readily flow off the aircraft surfaces and thus provide limited protection from formation of additional frost.
Anti-icing fluids are those that will prevent formation of frost and ice on surfaces over extended periods such as overnight and in the case of delays between departure from the gate and takeoff.
One approach to formulating anti-icing fluids is to add thickening agents to deicing fluids with the intention of increasing the viscosity of the fluid and thereby reducing its tendency to run off the surfaces of the aircraft. There are a number of thickened fluids which are commercially available. These include Kilfrost Anti-Icing Fluid ABC-3, SPCA AD-104, Union Carbide UC 5.1 and Octagon 40 below.
A good anti-icing fluid must be readily removed from the surfaces of the aircraft during takeoff. It should also have good rheological properties in that it must have sufficient viscosity to be retained on the aircraft surface yet require little force to be removed. It is also important that it can be applied with conventional spraying devices without causing undue shear instability and loss of thickening properties.
In addition, the agent should not have a tendency to thicken during storage, so that when it is applied it is too viscous for effective removal or that the gelling results in phase separation, causing a loss of anti-icing properties.
Other anti-icing compositions are known. For example, a liquid agent for deicing and protecting against icing-up is described in U.S. Pat. No. 4,358,389 by means of which it is possible, in particular, to free the metal surface of aircraft rapidly and completely from ice, hoar-frost, snow and the like and to protect the surface against further build-up for a relatively long period. The agent is essentially composed of several components, namely of (a) glycols, (b) water, (c) thickeners, (d) substances insoluble in water, (e) surface-active agents, (f) corrosion inhibitors and (g) alkaline compounds. The quantities are very specific in each case, the quantity of the components (a) and (b) being at least 94%, relative to the total weight of the agent. The pH value is 7.5 to 10. Component (c) is cross-linked polyacrylate thickeners described in that patent and in U.S. Pat. No. 2,923,692.
U.S. Pat. No. 4,744,913 describes an anti-icing and deicing agent, based on glycols and water and having cross-linked acrylic polymers useful as thickeners and also containing customary corrosion inhibitors, surfactants belonging to the group of alkali metal alkylarylsulfonates and a neutralizing agent to adjust the pH to a basic value.
The agent contains as a thickener, two selected cross-linked acrylic polymers in a specific ratio by weight to one another, namely a selected cross-linked acrylic acid/aryl amide or alkali metal acrylate/acrylamide copolymer in a ratio by weight of 2:1 to 10:1. The neutralizing agent may be one of three compounds, ammonia, monoethanolamine, diethanolamine and/or triethanolamine as the first alkaline compound, potassium hydroxide as the second alkaline compound and a third alkaline compound. The composition of that invention is claimed to have relatively low viscosity even at arctic temperatures and low shear rates which ensures rapid and complete runoff of the agent at the takeoff of aircraft even under extreme conditions.
In U.S. Pat. No. 4,954,279 there is disclosed a deicer and anti-icing composition comprising a microemulsion having a continuous phase and a discontinuous phase comprising: 5 to 85% by weight glycol, 5% to 95% water, 5.0% by weight water insoluble oil comprising 0.1 to 2.5% polar compound and the remainder including a thickening agent, an emulsifier, and alkanolamines. It is stated that the composition provides desirable viscosity and shear stability.
U.S. Pat. No. 5,118,435 discloses an antifreeze composition that can retain high viscosity as the composition is diluted with water, is claimed to have highly pseudoplastic rheology so that it would have desirable flow off characteristics and is relatively insensitive to temperature changes over the range -25.degree. C. to 20.degree. C. This composition contains an alkylene glycol component, a thickener blend with at least one polyacrylic acid and at least one copolymer of acrylic acid, a hydrophilic vinyl monomer and an agent to neutralize at least part of the carboxylic acid groups present in the polymers of the thickener blend.
Partially neutralized polymers of acrylic acid forming water swellable networks with high water retention capability and very fast kinetics of volume change have been reported by F. Schosseler, et al. in J. Dispersion Sci. Technol., Vol. 8, p. 321, 1987. Further information about polyacrylic acids may be found in R. B. Lochhead, et al., "Polyacrylic acid thickener: The importance of gel microrheology and evaluation of hydrophobe modified derivative as emulsifier." Polymers in Aqueous Media, J. E. Glass, Editor, Advances in Chemistry Series. #223.
It is known in the art to aminate long alkoxylated alkyl chains terminated by hydroxyl groups. U.S. Pat. No. 3,654,370 to E. L. Yeakey teaches the amination of polyoxyalkylene polyols.
U.S. Pat. No. 5,288,873 relates to a process for making novel polyetherdiamines containing a cyclic urea from imidazolidones. The products of that invention were useful alone or in combination with known polyoxyalkyleneamines as curing agents.
In the instant invention the polyetherdiamine of U.S. Pat. No. 5,288,873 is reacted with certain fatty acids to produce a polyetheramide surfactant, useful as a surfactant in glycol-water mixtures.
There is always a need in the art of thickened aircraft anti-icing compositions for improvements which allow for compositions exhibiting advantageous rheological properties and which under low shear conditions are relatively insensitive to temperature changes. Other advantageous properties are retention of high viscosity even if diluted with water and stability for relatively long periods to delay or avoid reapplications of the composition during departure holdovers.